Extracting user id from Facebook Javascript SDK session object

Question

I am using Facebook's Javascript SDK "FB.ui" to pull up an OAuth dialog. Once you click allow, I need to capture the session object, extract the user id and use it further in my script. For some reason I cannot get this working properly, I keep getting undefined, even though the session does exist.

<script src="http://connect.facebook.net/en_US/all.js"></script>
<div id="fb-root"></div>
<script type="text/javascript">
FB.init({
    appId  : '***************',
    status : true,
    cookie : true,
    xfbml  : true
});
FB.getLoginStatus(function(response) {
    if (response.session) {
        //do something
    } else {
        FB.ui({
            method: 'oauth',
            display: 'page',
            scope: 'email',
            perms: 'email'
        },
        function(response) {
            alert(response.session.uid); //returns underfined
        });
    }
});
</script>

Answer 1

So I got this to work as I would like. This may not be the best way, but after much digging around and frustration I hope this could help somebody with the same question get on the right track.

JS source:

FB.getLoginStatus(function(response) {
    if (!response.session) {
        //initiate FB OAuth js popup dialog
        FB.ui({
            method: 'oauth',
            display: 'page',
            scope: 'email',
            perms: 'email'
        },
        function(response) {
            if (response.session) { //if permission Allowed
                var thesession = response.session;
                var thesession = eval('(' + thesession + ')'); //decode json
                //POSTing to local file get.user_graph.php, to fetch user info
                $.ajax({
                    type: "POST",
                    url: "get.user_graph.php",
                    data: "client_id=<?php echo $appId; ?>&client_secret=<?php echo $secret; ?>&sessions="+thesession.session_key+"&type=client_cred&uid="+thesession.uid,
                    dataType: "text",
                    success: function(user_graph){
                        var user_graph1 = eval('('+user_graph+')');
                        alert(user_graph1.name); //users name
                        alert(user_graph1.id); //users id
                        alert(user_graph1.email); //users email
                        alert(user_graph1.link); //users profile link
                    }
                });
            } else {
                //if permission Not Allowed
            }
        });
    }
});

get.user_graph.php source:

//exchange our session for an access_token
define('POSTURL', 'https://graph.facebook.com/oauth/exchange_sessions');
define('POSTVARS', 'client_id='.$_POST['client_id'].'&client_secret='.$_POST['client_secret'].'&sessions='.$_POST['sessions'].'&type=client_cred');
$curl_token = curl_init(POSTURL);
curl_setopt($curl_token, CURLOPT_POST,1);
curl_setopt($curl_token, CURLOPT_POSTFIELDS,POSTVARS);
curl_setopt($curl_token, CURLOPT_FOLLOWLOCATION,1);
curl_setopt($curl_token, CURLOPT_HEADER,0);
curl_setopt($curl_token, CURLOPT_RETURNTRANSFER,1);
$token = curl_exec($curl_token);

$token_decoded = json_decode($token,true);
//get the user graph (personal info)
$user_graph = file_get_contents("https://graph.facebook.com/".$_POST['uid']."?access_token=".$token_decoded[0]['access_token']);
echo $user_graph;